Silicon photonics technology is extending its utilization from current low-medium volume application as multi-channel transceivers in data center interconnection, to a more common use as optical multi-chip modules (OMCM). Such OMCM are used in high bandwidth hardware platforms for chip to chip and board to board interconnects. OMCM integrates in the same package an electronic and photonic chip with reduced power consumption, high processing capacity and low footprint and may be used in high capacity switches for data centers and in big IP routers. In typical OMCM the signal processing is performed by an electronic chip while the I/Os are performed by a photonic chip which is interconnected with optical fibers.
A significant issue is providing removable optical connectors between the silicon photonic chip and an optical fiber array, e.g. single mode fiber array. The connector has to provide for many fibers (12 or more), and has to be suitable for mass production.
For example, the connector should be mounted during the packaging process by using standard assembly machines and be compatible with printed circuit board (PCB) soldering processes (e.g. withstanding high temperature (about 260 degree Centigrade) for a time duration of 30 to 60 seconds.
P. De Dobbelaere et al: ‘Packaging of Silicon Photonics Systems’, Proceedings of OFC 2014, paper W3I.2 describes a single mode ribbon fiber coupling to silicon photonics nano-waveguides. This is based on the use of an array of vertical grating couplers implemented in the silicon chip and the use of a glass V-block that holds the fiber array by means of V-grooves. The V-block is actively aligned to the grating coupler array and then it is bonded to the chip by an adhesive. The use of vertical couplers, a V-groove and a ribbon fiber pigtail has the disadvantage of not being compatible with a PCB soldering process in which, during a reflow soldering step, the optical module is attached to PCB pads. In addition, a complex mechanical interaction is required between the chip and the package due to the fact that the ribbon fiber is mounted on the chip vertically.
T. Barwicz, Y. Taira: low-Cost Interfacing of Fibers to Nanophotonic Waveguides: Design for Fabrication and Assembly Tolerances' IEEE Photonics Journal, Vol. 6 N. 4, August 2014 describes a polymer waveguide bridge that includes routing waveguides and an adiabatic coupler to connect a standard ribbon fiber connector to the nano-waveguides in the silicon chip. This does not use diffractive coupling elements. The polymer waveguide gap element has a room occupancy in the range of millimeters, which is comparable with the dimensions of a photonic chip.